Mattress base



FIG. 1 is a perspective view of the design.

FIG. 2 is a top plan view the design.

FIG. 3 is a right side view of the design.

FIG. 4 is a bottom plan view of the design.

FIG. 5 is a left side view of the design.

FIG. 6 is a front end view of the design.

FIG. 7 is a back end view of the design.

FIG. 8 is a perspective view of the design showing an open drawer.

FIG. 9 is a front right perspective view showing a second embodiment of the design. The left side and rear views, not shown, form no part of the claimed design; and,

FIG. 10 is a front right perspective view showing a third embodiment of the design. The left side and rear views, not shown, form no part of the claimed design.

Any broken lines in the drawing are for illustrative purposes only and form no part of the claimed design. 

CLAIM The ornamental design for a mattress base, as shown and described. 